Pumps adapted to spray liquid for cleaning windscreens of motor vehicles are already known. These pumps are sucking water or water added with detergent substances from a reservoir and are delivering it under pressure to one or more nozzles spraying it on the windscreen of said motor vehicle.
These pumps may be either hand operated, i.e. actuated directly by the driver and nowadays almost obsolete, or electrically controlled by a switch and operated by the electric current supplied by the battery of the motor vehicle and consisting of a centrifugal miniaturized pump actuated by a motor causing the pump impeller to rotate and sucking the liquid from the reservoir delivering it under pressure, generated by centrifugal force, to the conduit leading to the spraying nozzles.
This kind of pump has the drawback, in addition to a high manufacturing cost, of having a low pressure head because of the reduced dimensions of the impeller, so that eventual impurities which should be formed in the spraying nozzles, are not expelled and therefore it is easy that said nozzles become clogged, even during use and then they must be cleaned by hand.
Furthermore, because of the loss of a sealing ring which is necessarily of little size on shafts rotating at speeds near 10,000 rpm, these pumps often undergo irremediable failure, in view of the chemical composition of the cleaning additives mixed with water.
Electromagnetic pumps are also known in the art, wherein a piston is electromagnetically moved in the compression stroke and is returned to the starting position either by gravity, but this involves a particular position of the pump, or by use of a biassing spring. These types have the drawback that a position of the electromagnetic force is used either for spring compression or for lifting the piston weight which must be proportionally high in order to allow the return stroke by gravity.